Electrolytic process for preparation of metal carboxylate complexes

ABSTRACT

The invention relates to an electrolytic process for preparation of metal carboxylate complex comprising placing a semi-permeable membrane ( 18 ) between the electrodes in order to isolate the same. This membrane ( 18 ) prevents the migration of the metal ions from the anode to the cathode, thus increasing the metal ion concentration in the anolyte, leading to highly increased and faster formation of metal carboxylate complex.

FIELD OF THE INVENTION

The present invention in general relates to an electrolytic process forthe preparation of metal carboxylate complexes. More specifically, thepresent invention relates to use of a semi-permeable membrane betweenthe electrodes, which prevents the migration of precious metal ions tocathode thus increasing the metal ion concentration in the anolyte.

BACKGROUND AND PRIOR ART

The prior art has demonstrated that the presence of copper and silverions in an aqueous solution is useful as a disinfectant. Many in theprior art have used copper and silver ions in an aqueous solution as adisinfectant in water systems such as cooling towers, swimming pools,hot water systems in hospitals, potable water systems, spa pools and thelike.

Typically, the copper and the silver electrodes were connected to adirect current power supply. When the direct current was applied to theelectrodes, copper and silver ions were generated by an electrolysisprocess from the copper and silver anodes respectively within the water.In one example of the prior art, water was passed continuously throughan ion chamber having copper and silver electrodes. The water emanatingfrom the ion chamber contained the copper and silver ions generated bythe copper and silver electrodes within the ion chamber. The wateremanating from the ion chamber containing the copper and silver ions areused as a disinfectant in water systems such as cooling towers, swimmingpools, hot water systems in hospitals, potable water systems, spa poolsand the like. The copper and silver ions within the water systems actedas a disinfectant for controlling algae, viruses, bacteria and the like.

U.S. Pat. No. 6,197,814 discloses a disinfectant formulated byelectrolytically generated silver ions in the presence of citric acidreferred to as electrolytically generated silver citrate. Silver ionsare generated in a water based citric acid medium by using silver metalas the anode, under a required potential, whereby the silver ions aregenerated near the anode. As the potential is applied across theelectrodes, silver ion tends to migrate towards the cathode & getsdeposited thereon thus leaving less number of silver ions in theelectrolyte to form complex with the acid. Due to this, theconcentration of silver citrate complex formation is less thus requiringmuch more time to reach the desired concentration.

U.S. Pat. No. 7,732,486 discloses anhydrous silver dihydrogen citratecompositions comprising silver dihydrogen citrate and citric acid. Theanhydrous compositions can be prepared by freeze-drying. The preparationmethod of liquid SDC (Silver dihydrogen citrate) involves applying aD.C. potential across the electrodes. The patent further disclosesapplication of reversible current to reduce silver deposition on thecathode

There is a need for a process for preparation of metal carboxylatecomplexes which provides a stable ionic formulation which may beelectrolytically generated in a high concentration within a shortperiod.

SUMMARY OF THE INVENTION

The present invention relates to an electrolytic process for preparationof metal carboxylate complexes comprising the steps of:

-   -   i) Immersing at least one anode and at least one cathode at a        predefined distance in an electrolyte comprising carboxylic acid        and/or alkali metal salts thereof;    -   ii) Isolating the anode and the cathode from each other by        placing a semi-permeable membrane in between; and    -   iii) Applying an electric potential across the anode and the        cathode to generate metal ions.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the disclosure may be readily understood and put intopractical effect, reference will now be made to exemplary embodiments asillustrated with reference to the accompanying figures. The figurestogether with a detailed description below, are incorporated in and formpart of the specification, and serve to further illustrate theembodiments and explain various principles and advantages, in accordancewith the present disclosure where:

FIG. 1 shows a perspective view of the electrolysis tank with theelectrodes immersed in the electrolyte.

FIG. 2 shows a top view of the electrolysis tank.

FIG. 3 shows a typical anode used in the process of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The description of the specific embodiments will so fully reveal thegeneral nature of the embodiments herein that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of theembodiments as described herein.

This invention relates to improved methods to generatetransition/precious metal carboxylate complexes.

An embodiment of the invention relates to an electrolytic process forpreparation of metal carboxylate complexes comprising the steps of:

-   -   i) Immersing at least one anode and at least one cathode at a        predefined distance in an electrolyte comprising carboxylic acid        and/or alkali metal salts thereof;    -   ii) Isolating the anode and the cathode from each other by        placing a semi-permeable membrane in between; and    -   iii) Applying an electric potential across the anode and the        cathode to generate metal ions.

A typical electrolysis process of the present invention entails using anorganic acid as an electrolyte and using precious/transition metalelectrodes. The electrodes (anode (3) and cathode (4)) are preferablyformed from 99.99% pure metals. Use of high purity metal electrodesproduces high quality products having impurities ≦100 ppm. The metalanode (3) is preferably rotated by a geared motor arrangement (15). Theanolyte is continuously circulated using an anolyte circulation pump(21) and this circulation of the anolyte by magnetically coupled pumpensures that a uniform concentration of metal ion is maintained in theanolyte. In a specific example, the anode (3) is a circular disc mountedon a hollow shaft continuously rotating at 5-30 rotations per minute(rpm) and maximum area of the anode is immersed within the anolyte.

The electrolyte comprises carboxylic acids or their alkali metal salt.The carboxylic acid is selected from lactic acid, citric acid, tartaricacid etc. Similarly, the metal electrodes are selected from thetransition metals or precious metals such as Copper, Silver, Gold,Palladium, Platinum etc.

The anode (3) is spaced apart from the cathode (5) at a distance ofaround 10-30 mm under applied potential of 2-20V.

A semi-permeable membrane (18), preferably fixed onto a semi-permeablemembrane locking base (20), is placed in between the electrodes i.e. theanode (3) and the cathode (5). This membrane (18) prevents the migrationof the metal ions from the anode to the cathode, thus increasing themetal ion concentration in the anolyte, leading to highly increased andfaster formation of metal carboxylate complex.

A suitable D.C. power supply is utilized to supply a potential having avoltage of about 2 to 20 volts to the electrodes through the bus bars(Cathode bus bar (1) and Anode bus bar (2)). The metal ions generated atthe anode (3) react with carboxylic acid or its salts in the anolyte toform metal carboxylate complexes. The semi-permeable membrane (18)prevents the migration of the metal ions generated at the anode frompassing through to the cathode and hence these metal ions react with theanolyte forming metal carboxylate complexes in high concentrations. Thissolution may be further processed, to produce solid carboxylic complexby filtration & freeze drying. Desired concentration of ions can beachieved in the electrolyte by longer application of specific voltageand time.

For a quick production of metal carboxylate complexes, a series ofanodes & cathodes can be simultaneously used.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription that follows may be better understood so that the presentcontribution to the art can be more fully appreciated. Additionalfeatures of the invention will be described hereinafter which form thesubject of the invention. It should be appreciated by those skilled inthe art that the conception and the specific embodiments disclosed maybe readily utilized as a basis for modifying or designing otherstructures for carrying out the same purposes of the present invention.It should also be realized by those skilled in the art that suchequivalent constructions do not depart from the spirit and scope of theinvention.

EXAMPLES

Having described the basic aspects of the invention, the followingexample illustrates the specific embodiments thereof.

Example 1

This example illustrates the production of silver citrate complex.

The electrolysis tank (22) was filled with citric acid (AR grade) havinga concentration of 5-40 gms/liter made with high purity distilled water.The circular anodes (3) were made of high purity silver (99.99%) andmounted on an insulating shaft (4). The shaft was connected to a DCpower source through a carbon brush (12) & an electrical contact disc(13). Each anode is connected to the electrical contact disc (13)through a conductor. The current to the carbon brush is supplied throughan anode bus bar (2). The insulating shaft is mounted in a ball bearinghousing (9) having ball bearings (10) which was locked by a nut (11).The anode mounting shaft is coupled through a coupler (14) to a gearedmotor (15). The geared motor is mounted on a base plate (16) with amotor stand (17). The electrolyte was filled in the tank in such a waythat maximum anode surface is submerged inside the anolyte.Semi-permeable membranes (18) were placed between anodes & cathodes.These membranes (18) were locked to a bottom plate (20). The distancebetween the anode & the cathode was maintained at 27 mm. Cathodes (5)made out of high purity silver plates were hung from the hanger bar (6)in such a way that a constant gap is maintained between the anode & thecathode. Current was supplied to the cathode hanger bars through acathode bus bar (1). An anolyte circulating pump (21) was connected tothe drain plug (8) at the bottom of the tank for circulating the anolyteback to the tank through the plug situated at the upper side of thetank. This circulation ensured a uniform concentration in the anolytechamber. The shaft containing anodes were rotated at a constant speedvarying from 5-50 rpm. A potential of 2-20V was applied between theanode & the cathode with the help of a rectifier. The time ofelectrolysis was set with the help of a timer fixed in the rectifier.Silver ion concentration in anolyte was checked from time to time andwhen the desired concentration was achieved the electrolysis wasstopped, the anolyte filtered through a suitable filter mechanism toremove any suspended particles & stored in a tank protected from light.Fresh electrolyte was charged into the electrolysis tank for fresh batchof operation.

Other metal carboxylate complexes were also prepared according to theprocess in example 1.

The metal carboxylate complexes prepared by the present method havevarious applications. The applications include use as a disinfectant, anantimicrobial etc.

Table 1 shows various metal carboxylate complex concentrations whichwere prepared by the method described in example 1. and provides acomparative data with a metal carboxylate complex prepared by the priorart method.

TABLE 1 Metal Voltage carboxylate Carboxylic applied Time takenConcentration Prior Art Example Metal Acid (V) (hrs) (ppm) method 1Silver Citric Acid 2-20 8 5790 2400 ppm in 144 hrs 2 Silver TartaricAcid 2-20 V 2-6 hrs 9600 No data available 3 Gold Citric Acid 2-20 V 2-6hrs  5-30 No data available 4 Gold Lactic Acid 2-20 V 2-6 hrs  1-10 Nodata available 5 Palladium Citric Acid 2-20 V 2-12 1-5 No data available6 Palladium Lactic Acid 2-20 V 2-12  1-10 No data available 7 PlatinumCitric Acid 2-20 V 2-12 1-5 No data available 8 Platinum Tartaric Acid2-20 V 1-4  1-5 No data available 9 Copper Citric Acid 2-20 V 2-6  5000-15000 No data available 10 Copper Lactic Acid 2-20 V 2-121000-5000 No data available 11 Copper Tartaric Acid 2-20 V 2-6 1000-4000 No data available

1. A process for the preparation of metal carboxylate complex comprisingthe steps of: iv) Immersing at least one anode and at least one cathodeat a predefined distance in an electrolyte comprising carboxylic acidand/or alkali metal salts thereof; v) Isolating the anode and thecathode from each other by placing a semi-permeable membrane in between;and vi) Applying an electric potential across the anode and the cathodeto generate metal ions.
 2. The process as claimed in claim 1, where theanode is a rotating anode.
 3. The process as claimed in claim 1, whereat least 40% of the anode is immersed in anolyte.
 4. The process asclaimed in claim 1, where anolyte is continuously circulated.
 5. Theprocess as claimed in claim 1, where the at least one anode and the atleast one cathode is placed at a distance of 10 -30 mm.
 6. The processas claimed in claim 1, where the anode and cathode is preferably made ofsame metal.
 7. The process as claimed in claim 1, where the anode andthe cathode is made up of transition metals or precious metals selectedfrom Copper, Silver, Gold, Palladium and Platinum.
 8. The process asclaimed in claim 5, where the carboxylic acid is selected from citricacid, lactic acid, and/or tartaric acid.